UPDATE 1-Russia's Atomstroyexport enters CEZ nuclear tender

* Russian firm Atomstroyexport enters CEZ tender

* Tender could include work on up to 5 nuclear units

(Adds CEZ comment, background, more detail)

PRAGUE, Oct 30 (Reuters) - Russian nuclear engineering firm Atomstroyexport said on Friday it has submitted qualification documents to Czech power group CEZ (CEZPsp.PR) in a tender competition to build up to five nuclear reactors for the firm.

CEZ declined to detail how many companies submitted documents but said it expected to whittle down the contenders to a shortlist at the beginning of 2010.

In August CEZ launched a tendering for the construction of two nuclear reactor units at its Temelin power plant with an option for the utility to order up to three more nuclear units in other parts of Europe.

Atomstroyexport said it had submitted the documents by the noon deadline on Friday in a consortium also comprising Czech Skoda JS a.s. and Russia's Gidropress.

Westinghouse Electric, now a subsidiary of Japan's Toshiba Corp (6502.T), took over in the early 1990s as the main supplier for CEZ's last construction work at Temelin, which finished in 2000.

Potential rivals Areva SA (CEPFi.PA) and Siemens (SIEGn.DE), are among the contractors to supply Bulgaria's construction of its Belene nuclear plant.

Analysts have estimated the pricetag for the entire project of completing the Czech reactors at 500 billion crowns ($28.14 billion).

CEZ has not revealed the number of applicants, and Atomstroyexport is the first firm to make its interest known publicly. (Reporting by Jan Korselt and Michael Kahn, Editing by Greg Mahlich)